TCP/IPv6 Configuration and Management Manual (G06.24+)

Manage the NonStop TCP/IPv6 Subsystem
HP NonStop TCP/IPv6 Configuration and Management Manual—524523-008
6-4
Fault-Tolerant Operations, Ethernet Failover
Guidelines
TCP/IPv6 assigns the outbound traffic to the SUBNET assigned to that IP address.
Nonshared IP lets you control the inbound traffic load, forcing the connections to be
distributed over the two interfaces presented by the different IP addresses. This is
handy when you have limited hardware resources or you want to maximize the use of
LIFs. Both LIFs of a failover pair must be cabled to the same network segment. If
different IP addresses are used, the IP addresses must be on the same network
SUBNET.
When a shared IP failover pair is configured, NonStop TCP/IPv6 distributes new
sessions over the two LIFs of the pair. Similarly, each session is assigned one of the
LIFs from the pair for its outbound traffic.
A shared IP failover pair also requires that a second IP address, referred to as the
reserved IP address, should be configured on each SUBNET in the pair. This address
must be unique in the network and must reside on the same network subnet as the
shared IP address. NonStop TCP/IPv6 uses the reserved IP address when issuing
Address Resolution Protocol (ARP) requests to resolve the media access control
(MAC) address to an IP address. By using this reserved IP address, the ARP request
does not affect ARP table entries in other network devices that might currently have
sessions to the failover pair's shared IP address.
When an adapter failure or cabling problem is detected on one of the LIFs of a failover
pair, a gratuitous ARP packet containing the IP address of the failed LIF is sent using
the operational LIF. This causes all devices on the network segment that had ARP
table entries for this address to update their entries with the new MAC address of the
operational LIF. Traffic for all the sessions on the failed LIF migrates to the operational
LIF. When the failure is resolved and the failover pair is configured for nonshared IP,
NonStop TCP/IPv6 issues another gratuitous ARP packet on this LIF using its IP
address. This causes all the devices that have sessions to this IP address to change
their ARP table entries again and move the traffic to the new operational LIF. In shared
IP, the gratuitous ARP is not sent but new sessions are distributed over both LIFs of
the failover pair.
If configured for failover, during an adapter upgrade or removal, NonStop TCP/IPv6
detects the LIF unavailability and automatically moves traffic over to the associate LIF.
This feature eliminates the need for manual intervention for migrating traffic.
Reinsertion of a replacement adapter (of the same type and in the same slot)
automatically is detected and the replacement is initialized in the desired failover
configuration. Similarly, if a LIF fails, NonStop TCP/IPv6 detects it and moves traffic to
the associate LIF.
Note. If you have configured Ethernet failover as nonshared IP, you cannot have a failover pair
consisting of addresses on different SUBNETs. Also, you cannot mix adapter types in an
Ethernet failover pair.